[IMP] base, web: define landscape in report template

Since report refactoring the function to override is get_report_values
that only returns a dict of value that are used in rendering.
In order to render a pdf with a landscape orientation, a context key could
be added however since it's not possible to return a report object in
get_report_values, it's difficult to add a contexti without using some tricks.

This commit add a report option to use in the template that will be used
in order to modify the pdf orientation. The process used was already existing
for other options like dpi,...

addons/web/views/report_templates.xml

@@ -50,6 +50,7 @@
               t-att-data-report-margin-top="data_report_margin_top"
               t-att-data-report-header-spacing="data_report_header_spacing"
               t-att-data-report-dpi="data_report_dpi"
+              t-att-data-report-landscape="data_report_landscape"
               t-att-web-base-url="web_base_url">
             <head>
                 <meta charset="utf-8" />

odoo/addons/base/models/ir_actions_report.py

@@ -206,6 +206,9 @@ class IrActionsReport(models.Model):
         :param set_viewport_size: Enable a viewport sized '1024x1280' or '1280x1024' depending of landscape arg.
         :return: A list of string representing the wkhtmltopdf process command args.
         '''
+        if landscape is None and specific_paperformat_args and specific_paperformat_args.get('data-report-landscape'):
+            landscape = specific_paperformat_args.get('data-report-landscape')
+
         command_args = []
         if set_viewport_size:
             command_args.extend(['--viewport-size', landscape and '1024x1280' or '1280x1024'])